1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of Related Art
In a conventional image forming apparatus of an electrophotographic system, a density ununiformity occurs in a main scanning direction due to various factors including: a lean or dart of a charger which electrically charges a photoreceptor; a distance deviation between the photoreceptor on which a latent image has been formed, and a development roller which develops the image using a developer such as toner; an unevenness of conveyance amount of the developer which is conveyed by the development roller; and a difference among reflectance ratios in the main scanning direction of a polygon mirror which reflects laser light from a light source to the photoreceptor. As a result, a density ununiformity occurs over an entire surface.
Japanese Patent Application Laid-open No. 2007-264364 describes a conventional image forming apparatus which forms a plurality of patches having the same gradation at different positions in a main scanning direction on a rotating image bearing member (photoreceptor), measures the patches by a sensor provided in a machine, and corrects a gradation such that the obtained values become desired values, in order to output an image having a good gradation.
Japanese Patent No. 4147676 describes a technique to create a calibration file which stores gradation characteristic data for correcting a gray level of a printed matter in association with an output condition such as a print resolution in order to output an image having an appropriate gray level depending on the output condition, to correct the gray level based on the gradation characteristic data corresponding to the output condition when printing is executed, and when no gradation characteristic data corresponding to the output condition exists, to perform correction using gradation characteristic data corresponding to the output condition which is closest to an actual output condition.